Gas turbine engines, such as those used to power modern commercial aircraft, typically include a compressor for pressurizing a supply of air, a combustor for burning a fuel in the presence of the pressurized air, and a turbine for extracting energy from the resultant combustion gases. The combustor typically includes radially spaced apart inner and outer liners that define an annular combustion chamber. A number of circumferentially distributed fuel injectors project into the forward end of the combustion chamber to supply the fuel to the combustion chamber. One or more rows of circumferentially distributed air admission holes penetrate each liner to admit air into the combustion chamber.
There is an increasing emphasis on the reduction of gaseous pollutant emissions that form during the combustion process of gas turbine engines, particularly oxides of nitrogen (NOx). One approach to reduce NOx emissions is the implementation of a rich burn, quick quench, lean burn (RQL) combustion concept. A combustor configured for RQL combustion includes the following three serially arranged combustion zones: a rich burn zone at the forward end of the combustor, a quick quench or dilution zone downstream of the rich burn zone, and a lean burn zone downstream of the quench zone. By precisely controlling the fuel to air ratios in each zone, high-temperature excursions can be reduced and the resulting NOx emissions can be minimized. The effectiveness of the RQL concept, however, is primarily dependent on the design of the quick quench section of the combustor where the fuel-rich gases from the rich burn zone are rapidly mixed with excess air and passed to the lean burn zone. The design and development of the quench zone geometry is one of the challenges in the successful implementation of low-emissions RQL combustors. However, some of the quench zone features that reduce NOx emissions may have a corresponding adverse impact on other engine operating characteristics. For example, hole arrangements that optimize NOx emissions by rapidly mixing the fuel with air may reduce high altitude ignition performance.
Accordingly, it is desirable to provide a combustor that balances improved NOx emissions with other advantageous operating characteristics. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.